250 is plenty for most size deer. Shot placement is key. I try and place it right behind the shoulder. I preferably like to have the deer take that extra half step and expose all of it's vitals, but have no reservations about taking the standard broadside shot.

Bullets do make a difference, but nothing makes up for shot placement. I've been using XTPs for 10 years now and have never lost a deer with them. Most drop in their tracks or don't make it more than 10 yards. That being said, roundballs have and will continue to kill a lot of deer because they're placed in the right spot.